Carbon Dioxide/ AGM Examples Flashcards
Review the reaction process with carbon dioxide with soda lime.
When is the soda lime absorber most efficient?
Soda lime absorbs most efficiently when the moisture content is between 10-20%
Why is moisture essential for Carbon Dioxide Absorption?
Moisture is essential because the reactions take place between ions that exist only in the presence of water
What is true about carbon dioxide absorbents with low moisture content?
Absorbents with low moisture content exhaust rapidly
What can be added to increase the speed of Carbon Dioxide Absorption?
Activators (NaOH, KOH) added to increase speed of reaction
Why is KOH less common Carbon Dioxide Absorber?
KOH less common – implicated in reactions that produce carbon monoxide and compound A
How much heat and energy is released with Carbon Dioxide Absorption?
The overall exothermic carbon dioxide absorption reaction releases approximately 13,000 kcal of heat energy for every 22.2 liters (1 mole) of carbon dioxide absorbed
What temperatures within the soda lime can be reached with Carbon Dioxide Absorption?
Temperatures within soda lime can reach 45 to 50 degrees Centigrade
What is the average to maximum production of CO2 by anesthetized adult?
12-18 L/hr
What is the standard grandula size?
4 to 8 mesh is standard size for granules
Define four mesh granule.
A granule that will pass through a screen with four wires per linear inch
Define eight mesh granule.
A granule that will pass through a screen with eight wires per linear inch
What is true about the mesh number and the absorbent particle?
The higher the mesh number the smaller the absorbent particle
What is the property of large granules?
Larger granules have less resistance to flow but are less efficient secondary to smaller surface areas relative to their mass
What is added to effect the hardness and friability of granulas?
Inert silica and kieselguhr added to granules to increase hardness and decrease friability
What is present on each granula? What does it do?
Each granule has pitted pores to increase the surface area
What are the thre most important factors for absorbent granules?
- Size
- Porosity
- Nature of the granule surface
Review Carbon Dioxide Absorption: Granule Size.
Review Characteristics of Absorbents.
Table 16.5
What is the relationship of dust and Carbon Dioxide Absorption?
Dust (fines) from soda lime implicated in laryngospasm, bronchospasm and machine failure
What can all current carbon dioxide absorbents cause?
can cause irritation to mucus membranes
When does channeling occur?
Occurs in loosely packed canisters or when the canister design allows the gases to pass along the sides
What does gas take?
- Gas takes the path of least resistance
- Leads to exhaustion of granules exposed to gas flow
What needs to be done to prevent channeling?
Shake canister before installation into circle system
What indicated absorbent exhaustion?
Indicator dye is an acid or base that is added to the absorbent to signify absorbent exhaustion
What type of indicator dye is added to the carbon dioxide absorber to indicate exhaustion?
- Ethyl violet
- At a pH of 10.3 the ethyl violet changes from colorless to blue-purple
What can occur after exhaustion?
- No true regeneration
- Absorbent color reversion can occur after rest
What is the amount of reversion dependent on?
Amount of reversion dependent upon length of the rest period
Review clinical signs of carbon dioxide absorbent exhaustion.
Box 16.15
What do you do if granule exhaustion occurs during a case?
Steps to take for granule exhaustion during a case: increase FGF 1-2x MV & replace at end of the case
What does soda lime degrade?
Degrades most current volatile agents
What volatile agent is degraded the most?
sevoflurane
What volatile agent is degraded the least?
desflurane
What did the soda lime use to contain?
Historically contained a high amount of potassium and/or sodium hydroxide
What happens when soda lime is desiccated? (2)
- Exothermic degradation of inhalational agents
What can be produced by soda lime and sevoflurane?
Reaction with volatile anesthetic to form Compound A with sevoflurane
Sevoflurane _____ in soda lime
unstable
What does sevoflurance produce?
Produces compound A
What levels are compound A dangerous?
- Lethal at 130-340 ppm
- Produces renal injury at 25-50ppm in rats
What compound A levels are achievable in clinical practice?
Compound A concentrations of 25-50ppm are achievable in clinical practice
What can increase compound A levels?
Levels increase with increased absorber temperature, low flow rates, high sevoflurane concentrations, anesthetics of long duration, and absorbent dessication
What can help decrease the chance of compound A?
Product insert – Avoid fresh gas flows less than 1-2 L/min for more than 2 MAC hours
How is carbon monoxide formed?
Formed when desflurane*, enflurane or isoflurane pass through dry (dessicated) alkaline rich absorbents (e.g. potassium hydroxide, sodium hydroxide)
What can help decrease the chance of carbon monoxide formation (3)?
- Turn off oxygen at end of case
- Change absorbents regularly
- Use low flows to avoid drying
What do the bellows do?
Compressed gas (oxygen or air) serves as driving mechanism to compress bellows
What do ventilator relief valve maintains?
Ventilator relief valve (bellows pop off valve, spill valve, overflow valve) maintains circuit volume and pressure by releasing gas to the scavenger in the amount equal to the fresh gas flow per minute
When do bellows open?
Only opens during expiratory phase
What happens to inspiration to the driven bellows?
During inspiration driving gas closes the relief valve
What happens to the bellows when they open during expiration?
During expiration a weight in the relief valve holds the path to the scavenger closed until the bellows are filled
How much positive end expiratory pressure in the breathing circuit is generated with the bellows open?
Generates 2-3 cmH2O
What is the important difference between ascending/standing and descending/hanging bellows?
when there is a disconnection or a major leak the ascending/standing bellows will collapse
What happens when a disconnection occurs with descending/hanging bellows?
the ventilator will continue its up and down movements drawing in room air and driving gas during its descent and discharging it during the upward movement
How do you differientate between ascending/standing and descending/hanging bellows?
watching during expiration
What bellows rise during expiration?
Ascending bellows
What bellows descend during expiration?
descending bellows fall
What type of bellows are found in most AGM?
Most modern anesthesia machines have ascending bellows because they are thought to be safer